1. Field of the Invention
The present invention relates to camptothecin analogs which are useful as antitumor agents. More specifically, the invention is directed to water-insoluble and water-soluble derivatives of 10,11-methylenedioxy-20(RS)-camptothecin.
2. Discussion of the Background
Camptothecin is a pentacyclic alkalloid initially isolated from the wood and bark of Camptotheca acuminata by Wall et.al. (M. E. Wall, M. C. Wani, C. E. Cook, K. H. Palmer, A. T. McPhail, and G. A. Sim, J. Am. Chem. Soc., 94:388 (1966)).
Camptothecin is highly biologically active and displays strong inhibitory activity toward the biosynthesis of nucleic acids. Additionally, camptothecin exhibits potent anti-tumor activity against experimentally transplanted carcinoma such as leukemia L-1210 in mice or Walker 256 tumor in rats.
Several methods for the synthesis of camptothecin and camptothecin analogs are known. These synthetic methods include (i) methods in which naturally occurring camptothecin is synthetically modified to produce a number of analogs and (ii) totally synthetic methods.
U.S. Pat. Nos. 4,604,463; 4,545,880; and 4,473,692 as well as European Patent Application 0074256 are examples of the former type of synthetic strategy. Additional examples of this strategy can be found in Japanese Patents 84/46,284; 84/51,287; and 82/116,015. These methods require naturally occurring camptothecin which is difficult to isolate and hence these methods are not suitable for the production of large quantities of camptothecin or analogs.
Examples of a variety of totally synthetic routes to camptothecin and camptothecin analogs can be found in the following references: Sci. Sin. (Engl. Ed), 21(1), 87-98 (1978); Fitoterpapia, 45(3), 87-101 (1974); Yakugaku Zashi, 92(6), 743-6 (1972); J. Org. Chem., 40(14), 2140-1 (1975); Hua Hsueh Hsueh Pao, 39(2), 171-8 (1981); J. Chem. Soc., Perkin Trans 1, (5) 1563-8 (1981); Heterocycles, 14(7), 951-3 (1980); J. Amer. Chem. Soc., 94(10), 3631-2 (1972); J. Chem. Soc. D, (7), 404 (1970) and U.S. Pat. No. 4,031,098.
Synthetic studies directed to camptothecin analogs have also been conducted by the present inventors and are disclosed in J. Med. Chem., 23(5), 554-560 (1980); J. Med. Chem., 29(8), 1553-1555 (1986) and J. Med. Chem., 29(11), 2358-2363(1986) for example.
Water-solubility is an important criterion in developing potential antitumor compounds for pharmaceutical use. Most camptothecin analogs known in the art have relatively poor water-solubility. A need exists for additional water-soluble camptothecin analogs and methods for preparing the same.